A nuclear reactor core is formed from a multiplicity of fuel rods and other core component rods positioned in a multicluster skeleton framework having as many as 264 fuel rods. The fuel rods are pressurized with an inert gas. The high pressure in the fuel rods minimizes the possibility that the rods will collapse under the high pressures attendant a nuclear reactor core. The inert gas also increases heat transfer of the rods.
The fuel rods typically are manufactured from open-ended tubular rods. The fuel rods are made from a material having a low thermal neutron cross section such as a zirconium alloy while many core component rods are made from a more conventional stainless steel or other high alloy steel. One end of the rod is plugged and then girth welded by conventional tungsten inert gas methods. Fissionable pellets, or as with control rods, hafnium or boron neutron absorbent pellets, are inserted into the open end of the rod which then is plugged with a sealing plug. Depending on the design of the sealing plug, the fuel rod is pressurized through an axial opening located in the sealing plug or through pressurization slots located between the inner and outer clads conventionally found in some core component rods. After pressurization, the rods are seal welded to prevent depressurization.
However, during the initial girth welding operation used to weld the sealing plug to the fuel rod or to weld the ends of double clads together, sometimes the axial opening or pressurization slots are welded closed. Because the axial opening and pressurization slots are small in comparison with the fuel or control rods, and the rod end typically is contained in an enclosed glove or other pressurization or vacuum chamber during girth and seal welding, the fused axial opening or pressurization slots may not be noticed. As a result, the fused openings or pressurization slots prevent full pressurization of the rods. When the underpressurized rods are contained in a nuclear reactor core, the high pressures attendant the reactor core operation could collapse the rods and create reactor operational problems.
Heretofore, statistical process control has been used to determine the possibility that some welded fuel and control rods are underpressurized. Samples from select lots of fuel and core component rods are subject to destructive testing to determine if the rods are adequately pressurized. Based upon a statistical analysis of the results, groupings of fuel and control rods are rejected or accepted. However, one sample rod from a select rod lot is not representative of the quality of all rods in the lot. Accordingly, only individual testing of every welded fuel or control rod can give complete accuracy to determine whether rods are adequately pressurized. This is impossible as long as destructive testing is continued.
It is therefore an object of the present invention to provide an apparatus for determining pressurization in a nuclear fuel rod and the like without destructive testing.
It is a more particular object of the present invention to provide an apparatus for determining pressurization in a nuclear fuel rod and the like prior to seal welding the end of the rod.
It is still another object of the present invention to provide an apparatus for determining pressurization in a nuclear fuel rod and the like by measuring the increase in diameter of the rod occasioned by its internal pressurization.
It is still another object of the present invention to provide a gauge adapted for determining the increase in diameter of a tube or other rod-like object such as caused by pressurization therein.